Collapse-resistant swellable catheter

ABSTRACT

A catheter and method of making it are disclosed. The catheter includes a swellable inner element and a non-swellable outer sleeve covering an outer wall of the inner element. The inner element absorbs liquid from infusate administered through the catheter and swells in size. Outward swelling of the inner element is restrained by the non-swellable outer sleeve. The inventive catheter can be substituted for a conventional catheter that is used in an insulin infusion system.

FIELD OF THE INVENTION

The present invention relates generally to catheters and methods ofmanufacture thereof that improve the strength and functionality of thecatheters.

BACKGROUND OF THE INVENTION

A large number of people with diabetes use some form of daily insulintherapy to maintain close control of their glucose levels. Currently,there are two principal modes of daily insulin therapy. The first modeincludes syringes and insulin pens. These devices are simple to use andare relatively low in cost, but they require a needle stick at eachinjection, typically three to four times per day. The second modeincludes infusion pump therapy, via an infusion cannula (i.e., aninfusion needle or a flexible catheter), which requires an infusionpump. Infusion pumps, although more complex and expensive than syringesand pens, offer the advantages of continuous infusion of insulin,precision dosing, and programmable delivery schedules. This allowscloser blood glucose control which can result in improved healthoutcomes.

The use of an infusion pump requires the use of a disposable component,typically referred to as an infusion set, tubing set or pump set, whichconveys the insulin from a reservoir within the pump into the skin ofthe user. An infusion set typically consists of a pump connector, alength of tubing, and a hub or base from which an infusion needle orcatheter extends. The base has an adhesive that retains the base on theskin surface during use. The base may be applied to the skin manually orwith the aid of a manual or automatic insertion device. Often, theinsertion device is a separate, stand-alone unit that the user isrequired to carry and provide.

There are many available types of infusion sets incorporating varioustypes of infusion cannulas, including steel needle infusion sets andsoft catheter sets. Soft catheter sets can be inserted into a patientmanually with the aid of a steel introducer needle, which is laterremoved from the patient, leaving the soft catheter in place.Alternatively, a mechanized inserter can be used to insert theintroducer needle and catheter, after which the introducer needle isremoved. In either case, the introducer needle is completely removedfrom the infusion set before the infusion set is connected to theinsulin pump.

Another type of insulin infusion device is a patch pump. Unlike aconventional infusion pump and infusion set combination, a patch pump isan integrated device that combines most or all of the fluid components(including the fluid reservoir and pumping mechanism) in a singlehousing which is adhesively attached to an infusion site, and does notrequire the use of a separate infusion (tubing) set. A patch pumpadheres to the skin, contains insulin (or other medication), anddelivers the insulin over a period of time via an integratedsubcutaneous catheter. Some patch pumps communicate with a separatecontroller device wirelessly (as in one device sold under the brand nameOmniPod®), while others are completely self-contained. These devicesneed to be reapplied on a frequent basis, such as every three days, whenthe reservoir is exhausted or as complications may otherwise occur.

FIG. 1A illustrates an infusion set 1 for use with an infusion cannulasuch as a catheter 14. As illustrated in FIG. 1A, the infusion set 1comprises a fluid connector or hub 22 which is detachably attached to abase (10), a fluid tubing set 24 and a connector 26 which attaches to apump (not shown). Line set 20 includes the hub 22 and the fluid tubingset 24 is attached to or detached from the base 10, as in FIGS. 1B and1C.

FIG. 1B is a top view of the infusion set 1 with the hub 22 attached tothe base 10. An adhesive pad 18 is attached to the base 10 and isconfigured to be attached to the skin of the user. FIG. 1C illustrates aview of the infusion set 1 when the line set 20 is detached from thebase 10. The base 10 includes an infusion adapter 15 to which thecatheter 14 is attached.

FIG. 1D is a cross-sectional view of the infusion set 1 and more clearlyillustrates how the infusate is pumped into the catheter 14, which ispreferably made of a soft plastic material. The hub 22 of the line set20 includes a hub port 29 that receives the fluid tubing set 24. The hub22 includes a flow cannula 23 and a fluid channel 28 positioned betweenthe fluid tubing set 24 and the open tip 231 of the flow cannula 23. Thebase 10 includes a main base portion 12 to which the catheter 14 issecured. A pre-slit septum 16 encloses the adapter 15, when the hub 22is detached from the infusion base 10, as illustrated in FIGS. 1C and1E. When the hub 22 is attached to the base 10, the flow cannula 24penetrates the pre-slit septum 16 so that the fluid channel 28 is influid communication with the catheter 14. This allows infusate from thepump (not shown) to flow from the fluid tubing set 24 into the fluidchannel 28, and into the catheter 14, and the infusate exits the distalopening 141 of the catheter 14 into the patient.

Infusion cannulas for use in infusion sets and/or patch pumps aremanufactured of either rigid material, such as stainless steel, or softplastic materials, such as fluorinated polymers, including Teflon®.Infusion cannulas may be subject to kinking and occlusion.

A catheter can kink during or after insertion into a patient when thecatheter tube becomes bent due to various causes, resulting in arestricted flow of infusate exiting the catheter. Kinking can beconsidered to be the cessation of flow through a catheter due tomechanical causes, such as bending of the catheter, sliding back orfolding of the catheter on the introducer needle during insertion.

The restricted flow of the catheter can be caused by kinking and byother causes. In general, occlusion is the blockage or cessation of flowdue to biological, pharmacological or mechanical causes, includingkinking, and these failures typically occur during the use cycle.

Rigid catheters, such as stainless steel cannulas, may have a sharp tip,which is used to pierce the skin, similar to an introducer needle in aconventional inserter. Rigid catheters are recommended for individualswho experience a high incidence of kinking. However, such products arenot recommended for use beyond two days, because they can reduce sitepatency, due to tissue irritation.

On the other hand, soft plastic catheters, such as the catheter 14illustrated in FIG. 1D, may be prone to kink or occlude with normalwear, while rigid catheters (not shown) are often found to beuncomfortable to the user, since they tend to move around within thetissue.

In infusion devices, it is highly desirable to minimize the risks ofcatheter occlusion, kinking and other complications, while maintaining adegree of comfort to the user. Kinking and occlusion are described indetail below.

As noted above, kinking is considered to be the cessation of flowthrough a catheter due to mechanical causes. This failure mode can bethe result of insufficient interference between the inner diameter ofthe catheter and the outer diameter of the introducer needle duringinsertion. In addition, kinking can occur if a blunt distal end of thecatheter allows excess force to be transmitted to the catheter as thecatheter initially penetrates the outer surface of the skin. Similarly,excessive bounce or vibration in the insertion mechanization may resultin excessive force being transmitted to the catheter.

Kinking can also occur during the infusion or use cycle. A typical causeof this failure is the placement of the catheter into tissue whichundergoes significant movement during physical activity, which weakensthe structure of the catheter, making the catheter less likely to resistmechanical forces that may bend or twist the catheter. Damage thatcauses deformation of the catheter may also contribute to kinking.

There are many advantages to flexible catheters, including ease ofinsertion into a patient, user comfort, and reasonable cost. However,there can also be some disadvantages. Flexible catheters are generallymore susceptible to kinking than non-flexible catheters. The materialused in most flexible catheters is a polymer, such as Teflon®. Suchmaterial provides flexibility to the catheter. However, the flexiblenature of such catheters contributes to kinking because the walls ofsuch catheters are not rigid and are therefore susceptible todeformation due to movement of the catheter and/or the patient.

Accordingly, a need exists for an improved catheter design andconstruction that will improve the functionality of the catheter whileminimizing the disadvantages noted above. More specifically, a needexists to improve the design and construction of a flexible catheterthat maintains its flexible characteristics without the negative aspectsof the flexible design that contribute to kinking.

SUMMARY OF THE INVENTION

Objects of the present invention are to provide a flexible catheterconfigured and arranged to optimize column strength while maintaining orimproving its flexible characteristics and tensile strength, and withoutadversely affecting its ability to be inserted into and removed from apatient.

These and other objects are substantially achieved by providing aflexible catheter having a swellable inner tube surrounded by anon-swellable outer sleeve, in which the swellable inner tube swellsupon absorption of part of the infusate or other fluid that isadministered through the catheter, to increase the wall strength of thecatheter. This improves the catheter's resistance to kinking or othertype of blockage, while the outward expansion of the inner tube isconstrained by the non-swellable outer sleeve. The improved catheter canbe configured to optimize strength to avoid kinking and otherundesirable complications, while permitting insulin or other medicamentsto be administered via the catheter. The improved catheter can replace aconventional catheter without modification of the infusion set,insertion mechanism, or patch pump.

BRIEF DESCRIPTION OF THE DRAWINGS

The various objects, advantages and novel features of the presentinvention will be more readily appreciated from the following detaileddescription of exemplary embodiments thereof when read in conjunctionwith the appended drawings, in which:

FIG. 1A is a perspective view of an infusion set;

FIG. 1B is a top view of the infusion set of FIG. 1A;

FIG. 1C is a view of top view of the infusion set of FIG. 1A in whichthe line set is detached from the base;

FIG. 1D is a cross-sectional view of the infusion set of FIG. 1A;

FIG. 1E is a cross-sectional view of the infusion set of FIG. 1D, afterthe hub 22 has been removed from the base;

FIG. 2 is a perspective view of an exemplary catheter of the presentinvention, before expansion of the internal catheter;

FIG. 3 is a perspective view of an exemplary catheter, after substantialinward expansion of the internal catheter;

FIG. 4 illustrates another perspective view of the catheter of FIG. 2and a cross-sectional view thereof, before expansion of the inner tube;

FIG. 5 illustrates another perspective view of the catheter of FIG. 2and a cross-sectional view thereof, after substantial inward expansionof the inner tube;

FIG. 6 is a perspective view of an introducer needle that is insertedinto the catheter of FIG. 2;

FIG. 7 is an enlarged cross-sectional view of the catheter of FIG. 2before expansion of the inner tube;

FIG. 8A is an enlarged cross-sectional view of another catheterembodiment;

FIG. 8B is a view of the catheter of FIG. 8A illustrating certaindimensions;

FIG. 8C is an enlarged cross-sectional view of the inner tube of thecatheter of FIG. 2, with the inner tube shown partially swollen;

FIG. 8D is an enlarged cross-sectional view of the inner tube of thecatheter of FIG. 2, with the inner tube shown fully swollen;

FIG. 8E is an enlarged cross-sectional view of the inner tube of thecatheter of FIG. 8A, illustrating the size of the internal lumenrelative to that which would trigger a pump occlusion alarm;

FIG. 9A is a cross-sectional view of another exemplary catheterembodiment;

FIG. 9B is a cross-sectional view of another exemplary catheterembodiment, after the inner tube has become swollen;

FIG. 10A is a cross-sectional view of another exemplary catheterembodiment;

FIG. 10B is a cross-sectional view of another exemplary catheterembodiment, after the inner tube has become swollen;

FIG. 11A is a perspective view of a compression test that is conductedon the catheter of FIG. 2 by pressing the catheter between a probe and abase;

FIG. 11B is a cross-sectional view of the catheter of FIG. 2 with apartially swollen inner tube, prior to a compression test;

FIG. 11C is a cross-sectional view of the catheter of FIG. 11B duringthe compression test;

FIG. 11D is a cross-sectional view of a conventional catheter, prior toa compression test; and

FIG. 11E is a cross-sectional view of the catheter of FIG. 11B duringthe compression test.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

Although reference will be made to the exemplary embodiments depicted inthe drawings and the following descriptions, the embodiments disclosedherein are not meant to be exhaustive of the various alternative designsand embodiments that are encompassed by the present invention.

As illustrated in FIGS. 2-7, an exemplary embodiment of the presentinvention is a catheter 14 a that can function in the same manner as thecatheter 14 of FIGS. 1A and 1D. The catheter 14 a is composed of (1) aswellable inner tube 100 that is preferably produced from a swellablepolymer, and (2) an external, non-swellable outer sleeve 200 that ispreferably produced from a non-swellable polymer. The swellable innertube 100 can be replaced by structures other than a tube, as illustratedin FIGS. 10A and 10B. The non-swellable outer sleeve 200 is sized andshaped like the catheter 14 of FIGS. 1A and 1D.

In general, “swellable” in this context describes the ability of amaterial to absorb something, such as a liquid, and to swell in volumeor size due to the absorption. Absorption or non-absorption of liquidcan be targeted. For instance, one object may not be able to absorb aparticular liquid due to its composition and/or configuration, whileanother object may be able to absorb the same liquid and swell in sizeor volume. Such properties are effectively utilized in the presentinvention.

The swellable inner tube 100 of FIGS. 2-7 is preferably produced from aswellable polymer, such as polyurethane. More particularly, apolyurethane product such as Vialon™ biomaterial by Becton, Dickinsonand Company (BD) can be used to make the swellable inner tube 100 ofFIGS. 2-7 or the swellable segments 100 b of FIGS. 9A and 9B. Theswellable inner tube 100 will absorb a part of the liquid infusate thatis administered via the catheter, that it comes in contact with, toswell its volume. In an infusate containing insulin, Vialon™ biomaterialabsorbs the liquid solution in which the insulin is suspended, and notthe insulin itself. The liquid that is absorbed by the Vialon™biomaterial is mostly water. The amount and rate of swelling of theswellable inner tube 100 can be controlled by formulating itscomposition and providing various structures to produce the desiredcharacteristics. It is noted that insulin that is administered to apatient is typically in an aqueous solution with water content typicallybeing in excess of 95%, and the water is more readily absorbed by theVialon™ biomaterial.

For example, Vialon™ biomaterial can be formulated to control its degreeof swelling by absorption of liquid so that it can swell in size orvolume by 30% to 300%. Therefore, by careful selection of the materialformulation, the amount, volume and rate of swelling of the swellableinner tube 100 can be controlled. For illustrative purposes, inembodiments of the present invention, the maximum swelling of theswellable inner tube 100 is set at approximately 60%, but can be variedfor specific uses. Additional disclosures of the exemplary Vialon™biomaterial can be found in commonly assigned U.S. Pat. Nos. 5,226,899and 5,453,099 to Min-Shiu Lee et al., U.S. Pat. No. 5,545,708 to TheoOnwunaka et al., and U.S. Patent Application Publication No.2011/0054390 to Gary Searle et al., the entire contents, disclosure andsubject matter of each of the foregoing documents being expresslyincorporated herein by reference. The Vialon™ biomaterial polymerprovides compatibility with physiologic conditions, and Vialon™biomaterial polymer has the added advantage of generally not requiringprocessing additives such as antioxidants and detackifiers that may beextractable and therefore undesirable in biomedical applications.Vialon™ biomaterial is a thermoplastic polyurethane, and therefore itcan be thermoformed using techniques such as extrusion and injectionmolding.

The swellable inner tube 100 and the non-swellable outer sleeve 200combine to form a catheter 14 a that can function similarly to aconventional catheter in the delivery or infusion of insulin. Therefore,the catheter 14 a can be substituted for the catheter 14 of FIG. 1D, inan infusion delivery set as illustrated in FIGS. 1A-1D, or in a patchpump.

When the catheter 14 a is substituted for a conventional catheter in aninsulin infusion set or patch pump, in order to attach or insert thecatheter 14 a to the patient, an introducer needle 50 is inserted intothe swellable inner tube 100 of the catheter 14 a, as illustrated inFIG. 6. The combined catheter 14 a and introducer needle 50 are theninserted into the skin of the patient and the introducer needle 50 iswithdrawn while the catheter 14 a remains attached to the patient. Thisis similar to the conventional way of inserting a catheter of an insulininfusion set. During this process, the inner surface of swellable innertube 100 may come in contact with the introducer needle 50, but theswellable inner tube 100 is dimensioned so that there will not beexcessive interference with the introducer needle 50 to cause damage tothe swellable inner tube 50 or to the overall catheter 14 a.

The introducer needle shown in FIG. 6 may be a 27 g cannula, which has adiameter of 0.0163 in. The swellable inner tube 100 is sized andconfigured to accommodate the 27 g cannula. The inner diameter of thenon-swellable outer sleeve 200 can be 0.0248 in, the thickness of thethinner segments 140 can be 0.002 in, and the thickness of the thickersegments 120 can be 0.004 in, which will accommodate the introducerneedle 50.

Thereafter, insulin infusion or delivery to the patient via the catheter14 a takes place via the insulin infusion set (as illustrated in FIGS.1A-1D, for example) as desired, required and/or programmed. Multipleinfusions can take place before the catheter 14 a becomes occluded dueto some blockage caused by kinking or occlusion, after which thecatheter 14 a is detached from the patient and discarded.

It is noted that FIGS. 2-6 represent the catheter 14 a as a tubularstructure, for ease of explanation, but the end opposite to the distalopening 141 can be shaped to attach to an adapter (as in adapter 15 inFIGS. 1C and 1D). In other words, the catheter 14 a can have theexternal shape of a conventional catheter. Unlike the catheter 14 ofFIGS. 1C and 1D, however, catheter 14 a includes a swellable inner tube100.

When insulin infusion occurs, insulin is delivered to the patient viathe swellable inner tube 100, which, due to its constituent material(e.g. Vialon™ biomaterial), is able to absorb a part of the infusate(mostly water) that is administered to the patient. The amount absorbedis negligible and does not affect the desired insulin therapy,especially since insulin is generally not absorbed. FIGS. 2 and 4illustrate catheter 14 a prior to absorption of any infusate by theswellable inner tube 100. Upon absorption of a part of the infusate, theswellable inner tube 100 swells both inwardly and outwardly, asillustrated in FIGS. 3 and 5. As illustrated in FIGS. 3 and 5, theoutward swelling of the swellable inner tube 100 is restrained by thenon-swellable outer sleeve 200. Since outward swelling is restrained bythe non-swellable outer sleeve 200, the swelling or expansion of theswellable inner tube 100 is directed inward, as illustrated in FIGS. 3,5 and 8-10.

It is also desirable to control the direction of swelling of theswellable inner tube 100, since uncontrolled expansion may causediscomfort to the patient and have other undesired consequences, such ascreating bulges or weak points in the catheter 14 a that may cause arupture. In order to control the outward expansion of the swellableinner tube 100, an external, non-swellable outer sleeve 200 ispositioned around the swellable tube 100, as illustrated in FIGS. 2-7.The external, non-swellable outer sleeve 200 can be made of a materialthat will not significantly swell by absorption of liquid, such asTeflon® or similar polymers. The non-swellable outer sleeve 200 can befriction-fit, fused or otherwise connected to the swellable inner tube100 to form the catheter 14 a. It is also possible for the swellableinner tube 100 and the non-swellable outer sleeve 200 to be made as asingle unit, without assembling the two parts, via a co-extrusionprocess, for example.

The non-swellable outer sleeve 200, preferably made of Teflon®, will notsignificantly absorb liquid that it comes in contact with and will notsignificantly swell in size. The non-swellable outer sleeve 200 acts torestrain the outward swelling or expansion of the swellable inner tube100, as the swellable inner tube 100 swells upon absorption of liquid ofthe infusate. The non-swellable outer sleeve 200 is configured to havesufficient strength to retain the outward swelling or expansion of theswellable inner tube 100. For example, the strength of the non-swellableouter sleeve 200 can be increased by increasing its thickness.

It should be understood that the terms “swellable” and “non-swellable”are used in a relative and not absolute sense. For, example, thenon-swellable outer sleeve 200 can experience a small degree of swellingwhen exposed to infusate or body fluids, or even due to heat, as long asthe amount of such swelling is small enough to allow the outer sleeve200 to restrain the outward swelling of the swellable inner tube 100 asdiscussed above. In other words, the outer sleeve 200 can be somewhatswellable as long as it is less swellable than the inner tube 100. And,conversely, the inner tube 100 need not be swellable to a great degreeas long as it is more swellable than the outer sleeve 200.

As illustrated in FIG. 7, the non-swellable outer sleeve 200 ispreferably a thin-walled structure such as Teflon® shrink tubing with awall thickness of approximately 0.0005 inch, which is the differencebetween the inner diameter D1 and the outer diameter D2 of thenon-swellable outer sleeve 200. The outer diameter D2 and the innerdiameter D1 of the outer sleeve may be 0.026 in and 0.025 in,respectively. The non-swellable outer sleeve 200 is configured torestrain the outward expansion of the swellable inner tube 100 andrelated expansion forces, shown as arrows in FIG. 7. For such purpose,Teflon® shrink tubing of different thicknesses can be used for the outersleeve 200. Teflon® shrink tubing is commercially available having athickness as low as 0.00025 inch, and such shrink tubing can be used toform the external non-swellable outer sleeve 200.

When insulin treatment is started, infusate containing insulin is pumpedinto the catheter 14 a, and the swellable inner tube 100 beings to swellas liquid of the infusate is absorbed. The non-swellable outer sleeve200 prevents outward swelling or outward expansion of the swellableinner tube 100, from the perspective of the centerline of the catheter14 a, the swelling or expansion of the swellable inner tube 100 a isdirected inwardly, toward the centerline of the catheter 14 a andcircumferentially along the inner diameter D1 of the non-swellable outersleeve 200, in the directions of the arrows of FIG. 7.

The direction of swelling of the inner tube 100 can be controlled byconfiguring the swellable inner tube 100 to include alternating thickersegments 120 and thinner segments 140 and indents 142 on the thinnersegments 140, as illustrated in FIGS. 2 and 7. As the swellable innertube 100 swells in size, the thinner segments 140 become folded inwardlyat their respective indents 142, toward the centerline of the catheter14 a to form internal legs 146, as illustrated in FIGS. 3 and 5. Theformation of the internal legs 146 as the thinner segments 140 andthicker segments 120 swell in size increases the structural strength ofthe catheter 14 a. The indents 142 may run along the length of thethinner segments 140, as illustrated in FIG. 2, and one or more indentsmay be formed on the inner and/or outer surfaces of the swellable innertube 100 to control the manner and direction of the swelling of theinner tube 100. The swelling or growth of the thicker segments 120influences the movement and folding of the thinner segments 140 to formthe internal legs 146.

In addition, the swelling of the swellable inner tube 100 toward thecenterline of the catheter 14 a and circumferentially along the innerdiameter D1 of the non-swellable outer sleeve 200 is controlled so thatthe catheter orifice 160 formed along the inner surface of the swellableinner tube 100 remains open in order to permit infusate to be pumpedinto the catheter 14. When the inner tube 100 swells to its maximum sizeby the absorption of liquid infusate and/or body fluids it comes incontact with, as illustrated in FIGS. 3 and 5, even though thecross-section of the catheter orifice 160 has become reduced, theorifice 160 remains open so that insulin infusion can take place via theswellable inner tube 100, without triggering a blockage or back pressurealarm.

In the catheter embodiment illustrated in FIGS. 1-7, as more clearlyillustrated in FIG. 7, the cross-section of the swellable inner tube 100has six segments that resemble a hexagon. There are three thickersegments 120 alternately located between three thinner segments 140. Thethinner segments 140 have been further thinned or weakened at specificlocations, at indents 142, to control the movement of the segments 120,140 during swelling, and so that the thinner segments 140 fold inwardlyat the indents 142 to form internal legs 146. The segments 120, 140 andindents 142 preferably run substantially continuously and uniformlyalong the length of the swellable inner tube 100. Although a hexagonalarrangement for the swellable inner tube 100 is illustrated, there canbe more or less sides, while maintaining the objectives of strengtheningthe structural integrity of the overall catheter 14 a and maintaining asufficient catheter opening or orifice 160 to permit insulin therapy, asthe inner tube 100 swells in size.

FIGS. 8A and 8B illustrate cross-sectional views of another exemplarycatheter embodiment of the present invention. Catheter 14 b of FIGS. 8Aand 8B is similar to the catheter 14 a of FIGS. 2-7. Unlike theswellable inner tube 100 of FIG. 7, the swellable inner tube 100 a ofthe catheter 14 b includes thicker segments 120 a each having a concavesurface 122 customized to accommodate an outer surface of the introducerneedle 50. Such an arrangement can accommodate more swellable materialin the inner tube 100 a, as illustrated in FIG. 8A. Parts of thecylindrical outer surface of the introducer needle 50 are received atthe reciprocally shaped concave surfaces 122 of the thicker segments 120a, as illustrated in FIG. 8A. The thinner segments 140 of the swellableinner tube 100 a may also contact the introducer needle 50, asillustrated in FIG. 8A. As the thinner segments 140 can be made to besufficiently thin and flexible so that they may be pushed slightlyoutwardly by the introducer needle 50. In addition, indents 142 on thethinner segments 140 may be configured to reduce the resistance of thethinner segments 140 to the introducer needle 50.

FIG. 8B illustrates the catheter 14 b without the introducer needle 50.Exemplary dimensions for the catheter 14 b are provided as follows. Asillustrated in FIG. 8A, the outer diameter D1 of the non-swellable outertube 200 is 0.026 in, and the wall thickness T1 of the outer tube 200 is0.0005 in. As illustrated in FIG. 8B, the wall thickness T2 of each ofthe thinner segments 140 is 0.002 in, which is further reduced whereindents 142 are present. The wall thickness of the thicker segments 120varies as they conform to the inner diameter of the outer sleeve 200 asillustrated in FIG. 8B, but the thickness T3 of the thicker segments 120is 0.004 in. With further regard to each of the thicker segments 140,the radius R1 of its outer wall is 0.012 in and the radius R2 of itsinner wall is 0.008 in at the concave surface 122, which provides athickness of 0.004 in. In addition, the rotational angle A1 of each ofthe thinner segments 140 can be set at 45 degrees and the rotationalangle A2 of each of the thicker segments 120 can be 75 degrees, asillustrated in FIG. 8B to correspond to 60% expansion in the swellablematerial.

FIGS. 8C, 8D and 8E illustrate a cross-section of the embodiment ofFIGS. 8A and 8B without showing the non-swellable outer tube 200.However, it is noted that the actual swelling of the inner tube 100 atakes place within non-swellable outer sleeve 200. FIG. 8C illustratesan initial swelling of the inner tube 100 a, after the thinner segments140 have folded to form the internal legs 146. FIG. 8D illustrate theinner tube 100 a after it has completely swelled in size and cannotswell any further. In FIG. 8D, the internal legs 146 and the thickersegments 120 have increased in size to reduce the orifice 160.

FIG. 8D illustrates the swellable inner tube 100 a after swellingapproximately 60% in size. FIG. 8D illustrates the inner tube 100 aafter maximum absorption of insulin has taken place, while maintainingthe opening for the catheter orifice 160 that is sufficient toadminister insulin via the swellable inner tube 100 a of the catheter 14b. The controlled swelling of the swellable inner tube 100 a and itsinterface with the external non-swellable outer sleeve 200 improves thestructural integrity of the catheter 14 a, 14 b and to resist externalforces that contribute to catheter collapse, kinking or pinching.

In developing the present invention, analysis was conducted to determinethe increase in back pressure at the infusion pump resulting fromincreasing degrees of occlusion or blockage of the inner diameter of thecatheter. As the swellable inner tube 100 a swells in size due to liquidabsorption, the orifice 160 is reduced in size as it is displaced by theswelling of the inner tube 100 a. The analysis indicated that even a 60%reduction in the cross-sectional area of the catheter orifice 160resulted in only a minimal increase of 4 psi (pounds per square inch) inback pressure at the infusion pump.

In the example illustrated in FIG. 8E, the swellable inner catheter ismade of 60% swellable Vialon™ biomaterial and is shown with a catheterorifice 160 (the area inside the inner tube 100 a) having across-sectional area C1 of 0.00016076 in². After undergoing maximumswelling and fully forming the supportive, internal legs 146, asillustrated in FIG. 8D, the reduction in cross-sectional area of thecatheter orifice 160 is only 42%, and the uncompressed lumen space ismuch larger than the 0.0000241 in² cross-sectional area C2 (the areainside the innermost circle) illustrated in FIG. 8E, that would resultin the pump pressure increasing to where the pump would trigger anocclusion alarm or cause a loss of infusion therapy.

FIGS. 9A and 9B illustrate another embodiment of the inventive catheter.As illustrated in FIG. 9A, the catheter 14 c includes a swellable innertube 100 b. The swellable inner tube 100 b can be a composite structurewith three main swellable segments 125, equally spaced around the innerdiameter of the non-swellable outer sleeve 200, and thin connectivesegments 145 that connect the adjacent main swellable segments 145. Thecatheter orifice 160 includes lateral orifices 161 that are formedbetween the main swellable segments 125. The main swellable segments 125include leading surfaces 126 that will accommodate an introducer needletherebetween.

After the swellable inner tube 100 b absorbs liquid from the infusateand has swollen in size, as illustrated in FIG. 9B, the inner tube 100 bswells in size and catheter orifice 160, including the lateral orifices161, is reduced in size but remains open. The leading surfaces 126 ofeach of the main swellable segments 125 also increase in size such thatthey cannot fit into the opposing lateral orifices 161. As described inthe other embodiments, the main swellable segments 125 and the thinconnective segments 145 can be thinned or weakened at specific locationsto control the motion of expansion or swelling, and/or cause folding, asswellable inner tube 100 b swells as liquid from the infusate isabsorbed.

FIGS. 10A and 10B illustrate another embodiment of the inventivecatheter. In the catheter 14 d, there is no inner swellable tube, as inthe other embodiments. Instead, there are swellable segments 105 made ofa swellable material such as Vialon™ biomaterial that are not initiallyinterconnected, as illustrated in FIG. 10A. The swellable segments 105each include a thicker segment 125 and a pair of thin segment legs 145.The swellable segments 105 can be attached to the inner walls of thenon-swellable outer sleeve 200 a by various means. As illustrated inFIGS. 10A and 10B, the non-swellable outer sleeve 200 a includesretention tabs 210 on to which the swellable segments 105 are attached.The swellable segments 105 and the outer sleeve 200 a having retentiontabs 210 can be coextruded to form the catheter 14 d and cut to requiredlengths.

As the swellable segments 105 swell in size, adjacent ones of the thinsegment legs 145 swell and fold inwardly toward the orifice 160, asillustrated in FIG. 10B. The swelling of the thicker segments 125 alsourge the folding movement of the thin segment legs 145 and form across-section similar to the embodiments that are illustrated in FIGS. 3and 8D. Even after the swellable segments 105 have completely swelled insize, the catheter orifice or lumen 160 remains open to allowuninterrupted infusion therapy, while increasing the structuralintegrity of the catheter 14 d. In addition, as described in the otherembodiments, the swellable segments 105 can be thinned or weakened atspecific points to control the motion of expansion or swelling, and/orcause folding, such that the composite structure can form a customizedcross-section, after swelling is complete.

FIG. 11A illustrates a finite element analysis (FEA) in which thecatheter 14 b of FIG. 8A was subjected to simulated compression tests tocompare the force required to compress the inventive catheter 14 b, ascompared with a conventional catheter. In the FEA simulations, thecatheter 14 b was placed on a base 92 and a probe 90 was pressed on thecatheter 14 b at various stages of swelling of the swellable inner tube100, to view the resistance to the compression by the catheter 14 b.FIG. 11B illustrates the catheter 14 b, with the inner swellable innertube 100 a that has swollen in size such that the cross-sectional areaof the catheter orifice 160 has been reduced to about 42% of itsoriginal size, prior to compression by the probe 90. FIG. 11Cillustrates the catheter 14 b after a set compression force has beenapplied. The thickened walls of the swellable inner tube 100, due toswelling, and the configuration of the components thereof, such as thethicker and thinner segments 120 a, 140 and the formation of theinternal legs 146, resisted total collapse and maintained an opening ofthe catheter orifice 160 sufficient to administer insulin therapy.

In comparison, FIG. 11D illustrates a conventional catheter 220, beforethe application of the same set compression force in an FEA simulation.FIG. 11E illustrates the conventional catheter 220 after the setcompression force has been applied. The conventional catheter 220,having no internal support structures like the catheter 14 b, failed toresist the compression, resulting in a near-total collapse of thecatheter orifice 160, which would have triggered an occlusion alarm ifsuch collapse occurred during infusion therapy. The compression forcesimulates conditions which the catheter may be subjected to that wouldcause kinking and/or occlusion.

The finite element analysis indicated that the inventive catheter 14 bcan be expected to withstand approximately double the amount of forcethan a conventional catheter 220 before triggering an occlusion alarm.The force required to pinch to a minimum area before an occlusion alarmcan be triggered for the conventional catheter 22 was 0.334 lb., whilethe force required to pinch to a minimum area for the inventive catheter14 b was 0.660 lb.

The manufacture and assembly of the catheter 14 a, 14 b of the presentinvention will now be further described. A one-part swellable inner tube100, 100 a can be produced from a continuous extrusion process that iswell known in the art. The external non-swellable outer sleeve 200 canalso be produced from a continuous extrusion process. The externalnon-swellable outer sleeve 200 can be produced from a medical gradeTeflon® shrink tubing that can be manufactured with an inner diameterslightly larger than the outer diameter of the swellable inner tube 100,100 a, in order to allow the two pieces to be assembled together toallow a slip-fit assembly of the catheter 14 a, 14 b. The entirenon-swellable outer sleeve 200 can be shrunk in diameter, or just thelead end of the non-swellable outer sleeve 200 can be shrunk indiameter, to bind the two components to form the catheter 14 a, 14 b.Thereafter, the two-part assembly can be completed by Radio Frequency(RF) tipping to further bond the lead end of the external non-swellableouter sleeve 200 to the swellable inner tube 100, 100 a. Alternately,the swellable inner tube 100, 100 a can be molded to a finished lengthand tip dimensions, and the external non-swellable outer sleeve 200 canbe attached as described above. A similar process can form the catheter14 d of FIGS. 10A and 10B.

With regard to the composite catheter 14 c of FIGS. 9A and 9B, theswellable inner tube 100 b and the external non-swellable outer sleeve200 can be continuously extruded and/or co-extruded, using conventionalprocesses. Teflon® shrink tubing can be used to make the externalnon-swellable outer sleeve 200. The swellable segments 125, 145 of theswellable inner tube 100 b and the non-swellable outer sleeve 200 can beco-extruded and cut to desired lengths.

The swellable inner tube 100, 100 a, 100 b and the swellable segments105 can be co-extruded or two-shot molded, and the externalnon-swellable outer sleeve 200 can be attached to the swellable tube100, 100 a, 100 b or swellable segments 105 by the methods describedabove. The composite catheter 14 c of FIGS. 9A and 9B can be composed ofa non-swellable sleeve that is over-molded or co-extruded with segmentsof swellable polymer.

There are numerous advantages and improvements of the inventivecatheter, citing catheter 14 b as an example, over the conventional art.After the swellable inner tube 100 a becomes swollen, the overallstructure of the catheter 14 b is able to resist or minimize kinking,because the internal legs 146 that are formed as a result of thematerial swelling resist total collapse of the overall structure. At thesame time, the flow of insulin is possible through the catheter orifice160. Even though the cross-section of the catheter orifice 160 isreduced due to material swelling, a sufficient opening is maintained,such that the required pump pressure will not exceed the normal flowconditions of the pump and trigger an occlusion alarm.

Another advantage is that the inventive kink-resistant catheter 14 b ispotentially less expensive to produce than other anti-kinking catheterstructures, such as in-dwelling flexible stainless steel needles orpartially retracting introducer needles. Such alternative stainlesssteel needles are more rigid and can cause greater discomfort to thepatient.

Another advantage of the inventive device is that the overall dimensionsand gauge sizes of the collapse-resistant catheter 14 b, including theswellable inner tube 100 a and the non-swellable outer sleeve 200,conform to the gauge sizes currently used for insulin infusion, such asa 24 gauge introducer needle and a 27 gauge catheter. In other words,the catheter 14 b can be substituted for a conventional catheter used ininsulin infusion sets, without major modification. The advantagesmentioned above, with regard to catheter 14 b can generally be said ofcatheters 14 a, 14 c and 14 d, as well.

Although only a few exemplary embodiments of the present invention havebeen described in detail above, those skilled in the art will readilyappreciate that many modifications are possible in the exemplaryembodiments without materially departing from the novel teachings andadvantages of this invention. Accordingly, all such modifications areintended to be included within the scope of this invention as defined inthe appended claims and their equivalents.

What is claimed is:
 1. A collapse-resistant catheter comprising: aninner element; and an outer sleeve covering an outer wall of the innerelement; wherein the inner element comprises a swellable material; andwherein the outer sleeve comprises a non-swellable material.
 2. Thecatheter as claimed in claim 1, wherein the inner element absorbs liquidthat is administered via the catheter and swells in volume.
 3. Thecatheter as claimed in claim 2, wherein outward swelling of the innerelement is restrained by the non-swellable outer sleeve.
 4. The catheteras claimed in claim 2, wherein the swelling of the inner element isdirected inward toward its centerline.
 5. The catheter as claimed inclaim 1, wherein the orifice of the catheter is sized to receive anintroducer needle.
 6. The catheter, as claimed in claim 1, wherein theswellable material of the inner element comprises a swellable polymer.7. The catheter, as claimed in claim 6, wherein swelling of the innerelement is controlled by the polymer composition.
 8. The catheter asclaimed in claim 6, wherein the swellable polymer comprises Vialon™biomaterial.
 9. The catheter as claimed in claim 8, wherein swelling ofthe inner element is controlled by the Vialon™ biomaterial composition.10. The catheter as claimed in claim 1, wherein the non-swellablematerial of the outer sleeve comprises a non-swellable polymer.
 11. Thecatheter as claimed in claim 10, wherein the non-swellable polymercomprises Teflon® polymer.
 12. The catheter as claimed in claim 1,wherein the inner element comprises an inner tube having one or morethick segments and one or more thin segments.
 13. The catheter asclaimed in claim 12, wherein the one or more thick segments and the oneor more thin segments are alternately connected.
 14. The catheter asclaimed in claim 12, wherein each of the one or more thin segments isconfigured to collapse toward the centerline of the catheter, as liquidis absorbed.
 15. The catheter as claimed in claim 14, wherein each ofthe collapsed thin segments forms a support leg.
 16. The catheter asclaimed in claim 1, wherein the inner element comprises one or moreswellable segments attached to an inner surface of the outer sleeve. 17.The catheter as claimed in claim 16, wherein the outer sleeve comprisesone or more retention tabs on which the one or more swellable segmentsare attached.
 18. A method of administering insulin via a catheter,comprising the steps of: providing a catheter comprising a swellableinner element and a non-swellable outer sleeve covering an outer wall ofthe inner element; inserting the catheter into a patient; administeringinfusate to the patient via the catheter; absorbing liquid from theinfusate by the inner element to cause swelling of the inner element;and restraining outward expansion of the inner element by thenon-swellable outer sleeve.
 19. A method of making a catheter,comprising the steps of: forming an inner element by extruding aswellable material; forming an outer sleeve by extruding a non-swellablematerial; inserting the inner element into the outer sleeve; andshrinking the outer sleeve over the inner element to form the catheter.20. The method as claimed in claim 19, further comprising the step ofbonding the outer sleeve to the inner element.
 21. The method as claimedin claim 20, wherein the bonding step comprises RF tipping.
 22. Aninfusion system comprising: a base; a hub detachably attached to thebase; a pump; a fluid tubing set that connects the pump and the base;and a catheter comprising: a swellable inner element; and anon-swellable outer sleeve covering the outer wall of the tubing;wherein the swellable inner element is attached to an inner surface ofthe non-swellable outer sleeve.
 23. A patch pump comprising: a base; ahub detachably attached to the base; a pump; a fluid tubing set thatconnects the pump and the base; and a catheter comprising: a swellableinner element; and a non-swellable outer sleeve covering the outer wallof the tubing; wherein the swellable inner element is attached to aninner surface of the non-swellable outer sleeve.